Syrian rebels break their fast with the iftar meal during the Muslim fasting month of Ramadan in the northern city of Aleppo on 24 July 2012. Photograph: Bulent Kilic/AFP/Getty Images

4.55pm: Here's a summary of the latest developments relating to Syria.

• Aleppo, Syria's commercial capital, is braced for a major confrontation as hundreds of fighters from both sides stream into the city. Government forces are said to be deployed around the 13th century citadel, with thousands more on their way.

• The BBC in Aleppo and ITN in the Damascus suburb of Douma have both broadcast footage of Assad's forces bombing opposition strongholds with fighter jets. Both reporters described the sight and sound of jets as "unmistakable".

• Activists have released disturbing video purporting to show victims of a massacre in the Qaboun district of Damascus. The footage shows the bodies of 11 people, some of whom appeared to have been tortured.

• About half of the UN's 300 observers have left Syria, Hervé Ladsous, the head of UN's peacekeeping operations announced in Damascus. The new head of the mission Babacar Gaye, described the situation in Syria as "very difficult".

• Russian foreign minister Sergey Lavrov says the US reaction to last week's assassination of four members of Assad's inner circle amounted to an endorsement of terrorism.

• Israel's military chief of staff has warned that an attack on Syria's stockpile of chemical weapons could trigger a widespread conflict with international repercussions.

• Syria's envoy to the United Arab Emirates, Abdel Latif Al Dabbagh, has defected after his wife Lamia al-Hariri, who is Syria's the envoy to Cyprus, announced she was leaving Nicosia. The couple are reported to be in Qatar.

I was talking to the commander who is directing the fight for Aleppo. He's pretty bullish, he says about half of the city is under rebel control. He drew me a little map of Aleppo as a large cake with the south and northern suburbs, which he says the FSA has. But it's pretty clear they have been under massive attack from government forces, from helicopter gunship. When I was sitting with him, his phone rang and he claimed the rebels had succeeded in shooting down a helicopter.

If they [the regime] loose Aleppo, psychologically it would be devastating. It would be a bulkhead, a bit like Benghazi in Libya, which the rebels could use to push forward to capture Damascus.

The rebels feel the momentum is very much with them. Morale is extremely high, despite the fact that this is an asymmetric conflict - the rebels being this Dad's Army force with Kalashnikovs and hunting knives - they feel they are going to win. What they have, and what the regime lacks, is self belief.

The regime has almost totally abandoned the countryside, Luke claimed.

Where I am the FSA controls all of these rustic areas ... they are now pushing into urban areas, and they are taking casualties, but I think ultimately they will prevail. It would be foolish to predict the regime coming to an end in weeks, but I think we are definitely talking about months now not years.

The rebels are pretty organised, and they have got better. I was talking to one fighter called Bilal who was saying 'to begin with we just fired at tanks now we know to hit their rear tracks. We have got better at aiming'.

Paradoxically the Syrian army is scared. They have all this equipment, but they are extremely reluctant to take on the FSA head to head. They will shell them, but what they won't do is the street fighting.

This is now a "guerrilla style war" in which FSA seize districts, and then tactically retreat, before returning again, Luke said. In nearby Atareb the regime retreated after a week because they ran out of food, he said.

Last year I was in Libya during the fall of Tripoli. Libya was fairly clear cut, as a reporter when the rebels moved forward you moved forward. Here it is much more of a mosaic. Most of rural Syria is FSA controlled, but there are certain small villages and towns which are not. It's terribly fluid.

This is a revolt by Syria's rural poor. It's not just a sectarian conflict, it's more complex than that ... it's a popular upheaval against what in effect is a brutal military dictatorship which doesn't want to let go which knows its options are narrowing and will fight to the end.

4.17pm: An update on the "Omar Farouq Brigade" video calling for jihad in Syria (see 1.20pm). The Long War Journal, which translated the video, says the name refers to an al-Qaida operative who was killed in Iraq in 2006. A reader has emailed us disputing the alleged al-Qaida connection.

The reader says the name has nothing to do with al-Qaida but refers to the second caliph, Umar (or Omar), who is sometimes known as "al-Farouq".

Lebanon has sent a letter asking Syria to avoid incursions by its troops into Lebanese territory, foreign minister Adnan Mansour said today, according to a Reuters report. Several Lebanese civilians, including women and children, have been killed during border skirmishes.

Turkey has clarified that the border closure announced earlier does not apply to Syrian refugees, AP reports:

Turkish economy minister Zafer Caglayan said deteriorating security was behind the closure of a border through which Turkey once exported food and construction materials to the entire Middle East, though the volume of traffic had dropped 87% since the Syrian conflict began in March 2011.

"We have serious concerns over the safety of Turkish trucks regarding their entry and return from Syria," he said, adding that three border crossings were in rebel hands. Syrians seeking refuge or to resupply would still be allowed in.

Russian foreign minister Sergei Lavrov suggested today that al-Qaida elements had taken control of post on the Syria-Turkey border, Reuters reports:

"According to some information, these checkpoints were seized not by the Free Syrian Army at all - whatever one thinks about it - but by groups directly linked with al Qaeda," Lavrov said at a news conference with his Cypriot counterpart.

It's a really chaotic scene. They are unified by one goal, fighting Bashar al-Assad. But once that goals disappears you see the cracks emerging.

You see that very clearly in areas they control. Once they don't have a Syrian army to fight, once there is no security risk, all the differences start appearing on the surface. In a couple of places there have been clashes between battalions of the FSA.

Ghaith said the clashes have been over leadership and who controls the scarce supplies weapons.

People are fighting over these resources. Who is the legitimate force in a village? Who is the legitimate force in a town? These [questions] are creating so much friction between the units that they are fighting. It's kind of a secret, they don't want to talk about it but there are clashes happening ... clashes with RPGs, mortars, with hand grenades and kalashnikovs. It happened three weeks before I arrived in Deir el-Zour ...

Forming a uniform command structure is the real challenge for the FSA. In a small village I visited there were two military councils. You have a huge level of mistrust.

The diversity and scattered structure of the FSA is its strength but also its weakness, he claimed. "Even in Libya they [rebel forces] were more unified. Here the [opposition Syrian] National Council in Istanbul doesn't have the legitimacy amongst different group," Ghaith said.

Despite the infighting the rebels control 90% of Deir el-Zour province, Ghaith said.

We travelled for hours without meeting any government troops and any government checkpoints. Government checkpoints are concentrated around oil fields and military installations. For the first time the Free Syrian Army has more soldiers than the government forces. They do have control, yet they only have AK47 and RPGs. They cannot attack a bases because they don't have artillery they don't have tanks.

In reality they have safe havens [already] on the eastern side on the border with Iraq and on the northern side with Turkey.

Ghaith was in Deir el-Zour province last week as assassination attacks rocked the Assad regime in Damascus. He said that despite the chaotic scenes in the capital, the regime's showed its strength by continuing to fight in the east

Can you imagine this garrison fighting on the edge of the empire while Rome is burning. So I don't think the nerve structure of the regime has collapsed yet.

The key test for the FSA now is whether it can repeat its success in the countryside by taking control of key cities, he said. "I do see the endgame. The regime is crumbling."

1.40pm: Brazil has pulled "nearly all" its diplomats out of Syria on security grounds, the Rio Times reports. The paper quotes ambassador Edgard Casciano as saying things have become so bad in Damascus that "you simply cannot step outside there is so much shooting going on".

The embassy is in the Mezzeh district of Damascus.

The Rio Times adds that the number of Syrians applying for visas to go to Brazil has shot up to 395 so far this year, compared with 448 during the whole of 2011.

1.22pm: Israel's military chief of staff has warned that an attack on Syria's stockpile of chemical weapons could trigger a widespread conflict with international repercussions, writes Harriet Sherwood in Jerusalem.

Speaking to the Israeli parliament's foreign affairs and defence committee in Tuesday, Benny Gantz set out two options for possible Israeli military action on Syria's chemical arsenal, which the regime has admitted it possesses.

The first was a pre-emptive strike against weapons stores to prevent armaments falling into the hands of militant or jihadist groups. But, he said: "The possibility exists that we will find it difficult to pinpoint the exact place. If you work in a more spread-out fashion, you could very quickly find yourself in a wider conflict than you planned. What remains after we act and in whose hands [weapons] will fall must also be taken into consideration."

The second option was to wait until there was an attempt to move such weapons, and then launch a pinpointed strike on the convoy transporting them. This would require accurate and sophisticated intelligence gathering.

Israel has declared its intention prevent the transfer of chemical weapons to Hezbollah in Lebanon. Such a move would be a "casus belli," foreign minister Avigdor Liberman said on Tuesday.

Gantz told politicians that he believed the Syrian regime had taken recent steps to secure its weapons depots. "To the best of my judgment, for now, [President Bashar] Assad has control over his chemical weapons stockpiles, and he has upgraded the protection around them. These weapons have not yet been transferred into negative hands, but that doesn't mean it won't happen."

Israeli commentators in the main interpreted the chief of staff's remarks as favouring a pinpointed strike. Writing in Israel Hayom, Yoav Limor said:

Without going into detail, Gantz is saying the following, freely translated: In order to act effectively against Syria's strategic weapons systems (which include not only chemical weapons stockpiles but also advanced anti-aircraft weapons, long-range missiles and surface-to-sea missiles), a broad, noisy preemptive campaign would be necessary.

On the way, it will be necessary to overcome air defense systems, bases and guards, meaning a great deal of fire and many casualties. Assad will certainly not be able to accept such an offensive, and will be forced to carry out a painful response.

Syria hinted on Monday that it would respond to an "external attack" by use of chemical weapons. Even if it refrains from doing so, it still has enough weapons at its disposal to drag Israel into a painful confrontation.Israel has no interest in war with Syria—certainly a war that could strengthen Assad and extend his stay in power—and therefore the relevant option at present is a pinpointed operation. It is assessed that a strike on a lone convoy could pass "under the radar" and would not drag the other side into a response.

1.20pm: A video is circulating in the name of the "Omar Farouq Brigade" which urges Muslims to join a "jihad" against the Assad regime's forces.

The video is entitled "Turkish mujahideen who are conducting jihad in Syria". The Long War Journal, which translated its content, explains:

A speaker in Turkish exclaims, "O Muslims, o believers, where are you? Let's fight together to save Syria, Somalia and Afghanistan ..." The video then shows images of jihadi training camps in Syria, which they say include Turkish fighters, while a Turkish song, "Headed to Damascus," plays in the background.

The video closes with the declaration (spoken in Arabic with Turkish subtitles): "We are soldiers of the Omar Farouq Brigade in Syria ... and we raise our voice against Assad's barbaric army. We will live free on these lands! ... God help us!"

The Long War Journal says it is unclear whether the Omar Farouq Brigade mentioned in the video is the same as the al-Farouq Brigade, which is one of the most active units of the Free Syrian Army.

• Activists have released disturbing video purporting to show victims of a massacre in the Qaboun district of Damascus. The footage shows the bodies of 11 people, some of whom appeared to have been tortured.

• About half of the UN's 300 observers have left Syria, Hervé Ladsous, the head of UN's peacekeeping operations announced in Damascus. The new head of the mission Babacar Gaye, described the situation in Syria as "very difficult".

• Russian foreign minister Sergey Lavrov says the US reaction to last week's assassination of four members of Assad's inner circle amounted to an endorsement of terrorism. His ministry also dismissed the EU's latest sanctions against Syria as counter productive.

• Syria's envoy to the United Arab Emirates, Abdel Latif Al Dabbagh, has defected after his wife Lamia al-Hariri, who is Syria's the envoy to Cyprus, announced she was leaving Nicosia. The couple are reported to be in Qatar.

• The BBC in Aleppo and ITN in the Damascus suburb of Douma have both broadcast footage of Assad's forces bombing opposition strongholds with fighter jets. Both reporters described the sight and sound of jets as "unmistakable".

12.22pm: Very disturbing footage has emerged showing the victims of what activists claim was a massacre in the Qaboun district of Damascus.

The regime's army committed a new massacre against unarmed civilians who had hidden in a shelter due to fear of the shelling. After shelling, which had targeted the neighbourhood for the past 5 days, regime forces detained more than 150 people from one of the shelters. The detainees were taken to military police and threatened with death. Their bodies were found yesterday in the area of Tishreen neighbourhood, some were executed and others were killed due to the shelling.

Footage showed 11 bloodied bodies, some in an alleyway and some inside a building. Three appeared to have been shot through their shirts, which were pulled above their heads, and one was kneeling against a wall.

Rania al-Midani, an opposition activist who lives near Qaboun, said that the men were arrested five days ago in a nearby district.

"Activists found them today in Tishreen alley. They thought these men were in jail. They could only enter the alleyway today to find their bodies as it was previously occupied by (pro-Assad militia) shabbiha," she told Reuters over Skype.

11.47am: Could this be why Manaf Tlass was out of the limelight for a while? There are claims that he was on umrah (the lesser pilgrimage) in Mecca, purging his sins.

Babacar Gaye, the new head of the mission, described the situation in Syria as "very difficult".

In the mission's remaining 27 days he said "every effort will be seized to alleviate the suffering of the population".

11.23am: Russian foreign minister Sergey Lavrov says the US reaction to explosions in Damascus amounts to an endorsement of terrorism. In remarks at a press conference in Moscow, reported by Russia Today, he said:

This is direct endorsement of terrorism. How are we supposed to understand that?

This is a sinister position, I cannot find words to express our attitude towards that.

In other words this means "We are going to support such acts of terrorism until the UN [security council] does what we want".

Reuters says Lavrov was referring to what he said were comments by US State Department spokeswoman Victoria Nuland that last week's attack which killed senior regime figures was not surprising given the Syrian government's conduct.

10.49am: Blogger Brown Moses has been studying videos of the fixed-wing aircraft seen circling over Aleppo yesterday – and he doubts that the warplanes were Russian-made MiGs.

The images are not very clear but he suggests that the shape more closely resembles the Czech-designed Aero L-39 Albatros, which is a jet trainer aircraft.

10.32am: More detail on the defection of Lamia al-Hariri, the Syrian envoy in Cyprus.

Two sources in the Syrian opposition have told Reuters that Hariri left the diplomatic mission in Nicosia on Tuesday, telling staff she was feeling unwell and was going to a doctor.

She is now reported to be in Qatar.

10.15am: Russia has condemned the EU's latest sanctions against Syria as "counter productive" and said it would not recognise the EU's attempts to impose an air and sea blockade.

Russia's foreign ministry tweeted:

The sanctions adopted by the EU Foreign Affairs Council are essentially an air and sea blockade against #Syria

9.56am: Tribes are an ancient feature of Syrian society, neglected and exploited for decades by the Baathist regime in Damascus. They are now coming to the fore again, and can be expected to play an key role in the country's post-Assad future, Hassan Hassan writes in an article for Comment is free.

He argues that Nawaf al-Fares (pictured), the Syrian ambassador in Iraq who defected recently may be the most important defector so far, since he is also an important tribal figure.

Unlike other opposition figures who have little power base in Syrian society, Fares leads a powerful clan in the east of the country. His clan is part of the Egaidat tribal confederation, the largest and most prominent in that area, with at least 1.5 million members across 40% of Syria's territory. It also has kinship links to Saudi Arabia, Kuwait and Qatar.

The Arab Gulf states' aggressive stance towards the Assad regime has been driven by these ties as well as by their anti-Iranian sentiment. From the early weeks of the uprising, members of the Syrian tribes in Deraa were appealing to their "cousins" in the Gulf to help them.

From the Gulf to Iraq to Syria, the area is interlinked in a complex web of tribal relations. The Syrian tribes originated in Arabia and moved north with the Muslim campaigns in the seventh century and later in search of water and grazing for livestock.

9.40am: We now have a video of Manaf Tlass's defection speech which was broadcast last night on the Saudi-owned al-Arabiya TV channel.

His speech has had a mixed reception on Twitter. Some view it as a significant step:

Manaf Tlass was not speaking to the opposition or to the people of #Syria: he was placing a call to his peers in the army.

Allow me to serve Syria after [President Bashar] al-Assad's era. We must all unite to serve Syria and promote stability in the country, rebuilding a free and democratic Syria. Allow me to call on a united Syria ... [The] new Syria ... should not be built on revenge, exclusion or monopoly.

First came an unmistakeable sound that has so far been absent in this conflict - the roar of fighter jets. What appeared to be Russian-made MiG planes arced through the sky.

We watched as they dropped in, bombing and strafing rebel positions. Dead and wounded civilians and fighters were taken to hospitals and makeshift clinics as the human cost of this conflict continues to grow.

Like Pannell, Neeley described the sight and sound of jets as "unmistakable". He reported: "This is the first time we can categorically say the Syrian airforce has been deployed here. President Assad is now using warplanes against his own people in this built up area."

We have to work closely with the opposition because more and more territory is being taken and it will, eventually, result in a safe haven inside Syria which will then provide a base for further actions by the opposition. And so the opposition has to be prepared. They have to start working on interim governing entities ... We do believe that it is not too late for the Assad regime to commence with planning for a transition, to find a way that ends the violence by beginning the kind of serious discussions that have not occurred to date.

We urge you to take immediate steps, in close and continuing consultation with the Congress, to work with regional partners to establish air-patrolled "safe zones" covering already liberated areas within Syria, using military power not only to protect these zones from further aggression by the Assad regime's military and irregular forces, but also to neutralise the threat posed by the Syrian dictatorship's chemical and biological weapons ...

America's continued inaction in Syria risks becoming what you called in your 2009 Nobel Prize acceptance speech, "complicity in oppression," and only serves to undermine our interests and embolden our enemies.

Three of the four new security nominations are Sunnis. There is debate on the fourth (Abdul Fattah Qudsiye), who may be either Sunni or Druze. All are hawks. The notorious Rustum Ghazali, who ruled Lebanon with an iron fist, is among them. The message is that Sunnis will dominate the security leadership. This is an effort to keep the Sunni-Alawi alliance alive. Baathist rule has been built on the Sunni-Alawi alliance, which has all but collapsed since the beginning of the uprising. The defections of high level Sunnis recently underscores that it is moribund.